Electrical activity plays key roles during neuronal development including regulation of process outgrowth, synapse formation and patterns of gene expression. Our long-term goal is to define the mechanisms and molecules that direct cell-type specific and developmentally regulated expression of ion channel genes that are essential for rapid signaling of electrically excitable membranes. Our recent work has demonstrated that despite uniformity in the biophysical properties of voltage-dependent potassium current in spinal neurons, expression of voltage-dependent potassium (Kv) genes is heterogeneous. The hypothesis underlying this proposal is that members of 3 different potassium channel gene subfamilies (Kv1 alpha, Kv2 alpha and Kv beta) contribute to the voltage- dependent potassium current of different spinal neuron subtypes, Kv1 alpha and Kv2 alpha are pore-forming subunits, whereas Kv beta is an auxiliary subunit associated with Kv1 channels. There are 4 Specific Aims: 1) Identify the Kv1 alpha subunit isotypes that are expressed in Xenopus embryonic primary spinal neurons. 2) Examine the role of auxiliary Kv beta subunits in developmental regulation of Kv1 currents. 3) Determine the contribution of Kv2 alpha subunits to the endogenous voltage-dependent potassium current. 4) Identify the potassium channel Kv1 alpha, Kv2 alpha and Kv beta subunits that contribute to voltage-dependent potassium current in specific neuronal subtypes. A combination of embryological, electrophysiological, molecular biological and immunological techniques will be used to fulfill these Aims. The experimental preparation - the Xenopus embryo provides an ideal system for analysis of gene function in embryonic neurons, because manipulation of gene expression is easily achieved by microinjection of RNA. The information provided by these studies will allow us to define the role of electrical excitability in differentiation and function of the emerging nervous system, leading to the potential treatment of developmental disorders of the brain.